High powered flip-chip packages require thermal dissipation from the back side of the semiconductor chip. Heat has been dissipated from semiconductor chips by the use of heat spreaders connected to the lead frame die bond pad, or through thermally conductive, and electrically nonconductive epoxy materials. This method is shown in U.S. Pat. No. 5,510,649 where the semiconductor die is first connected to an insulating layer of material which is then bonded to a heat spreader by an epoxy.
Thermal grease has been used to transfer heat from the semiconductor die to a heat spreader. In U.S. Pat. No. 5,442,234, a heat sink is attached to one side of a die-attach paddle using a layer of thermal grease between the heat sink and the die attach paddle. In this method, the thermal grease is applied to one side of the die attach paddle and the semiconductor die is attached to the opposite side of the die attach paddle.
In U.S. Pat. No. 5,289,337, flip-chip devices have been glued directly to a heat spreader by a thermal conductivity and low modulus cement. One or more electrically passive thermal shunt chips are disposed between the substrate and the heat spreader plate for heat conduction. In one embodiment, thermal grease is interposed between the heat spreader plate and the semiconductor chips.
The ability of thermal grease to transfer heat from flip chip devices is limited and mechanical adhesion over the life of the device with thermal grease is questionable. Also, when thermal grease is used, an additional material is required to adhere the package lid to the device after the thermal grease is applied to the package.